Ink jet printing is a non-impact method for recording information in response to an electronic signal, such as that generated by a computer. In the printer, the electronic signal produces droplets of ink that are deposited on a substrate or media such as paper or transparent film. Ink jet printers have found broad commercial acceptance due to their reliability, relatively quiet operation, graphic capability, print quality, and low cost.
In current ink jet printing applications, several inks (typically black, cyan, magenta and yellow) are used to print textual and graphic information on a printing medium, typically ordinary paper. The inks primarily are composed of water, and contain a colorant that may be a dye or pigment dispersion. Pigment dispersions are preferred since the dyes are highly soluble and tend to smear upon handling, with the pigment dispersions offering improved water and smear resistance, as well as better light stability. The inks also generally contain a polyhydric alcohol to prevent nozzle clogging, and may contain various adjuvants. Such inks and ordinary paper are well suited for desk-top publishing, as currently practiced, wherein only a small portion of the paper receives printed text and graphic information.
It also is desired to reproduce high quality colored pictoral information (such as photographs and the like) using ink jet technologies for applications such as commercial printing and desk-top publishing. In these applications, however, the printing medium will receive substantially more of the black and colored inks to accurately reproduce the various hues, tints, and colors contained in a typical colored picture. For example, the printing medium will be expected to receive up to 200% or more coverage in conventional commercial printing.
Ordinary paperstock is not suitable for such high quality applications for a number of reasons. Water disrupts the paper structure, causing "cockle" that affects appearance of the paper and, in extreme cases, may actually cause the paper to distort to the extent that it contacts the ink jet pen, disrupting the printing process. Also, the paper may not absorb water sufficiently quickly to achieve the desired printing speed, or may cause flooding of the paper surface, which adversely affects image quality. Moreover, wicking of ink into the paper may cause the paper to "show through" into the printed image, detracting from image quality. There also is a need for the printed text and pictures to be more robust; e.g., exhibit better handleability, water fastness, and smear resistance after printing. Accordingly, there is a need for improved printed images produced by ink jet printing in general, and particularly for applications of ink jet printing technologies to commercial printing and for reproduction of pictorial information.
U.S. Pat. No. 5,006,862 discloses improved water-fastness and smear resistance of prints from inks using reactive dyes in which the reactive moiety is attached to the chromophore and treated with a strong base solution. The reactive moiety is capable of forming a covalent bond to the paper substrate.
U.S. Pat. No. 4,694,302 discloses a method of increasing the water-fastness and print quality of an ink in ink jet printers by providing a reactive species that reacts with a component in the substrate (i.e. paper) to form a polymer that binds the dye in the ink to the polymeric lattice. Alternately, a separate reactive component may be deposited on the substrate on the same location as the reactive species which causes the polymeric reaction to occur. This can result in making the dye image somewhat waterfast, but does not provide a durable print, since the media in non-image areas is not altered. This method is also limited to the use of certain papers or dyes.
U.S. Pat. No. 5,141,797 discloses an ink jet paper comprising a water-soluble polymeric binder, a titanium chelate crosslinking agent and an inorganic filler. The crosslinking agent crosslinks the binder to prevent dusting off of the pigment from the ink jet paper's surface. The crosslinking occurs during preparation of the media, ie. during drying, which is prior to application of the ink jet ink to the paper.
Current special ink jet media employ vehicle absorbrive components, and optionally additives, to bind the dyes to the media. The purpose is to provide reduced bleed, whereby the intrusion of one color into an adjacent color is minimized. As a consequence current media are inherently moisture sensitive, can be quite fragile to handling, and are subject to finger smearing. Moreover, the vehicle absorptive components usually consist of water-soluble polymers which results in slower printing speeds. In addition the water absorptive components leave the paper quite sensitive to moisture and smearing.
Thus, a need exists for an ink-media set that will provide a printed image having improved durability, water-fastness, and smear resistance in both imaged and non-imaged areas. A specific need exists for such an ink-media set capable of reproducing colored pictoral information in high quality, thereby meeting the demanding requirements of commercial printing.